FoxP3 transcription factor expressing regulatory T (Treg) cells are instrumental for the maintenance of self tolerance3. While all murine FoxP3 expressing CD4+ T cells are considered effective Treg cells, their human counterpart are heterogeneous in phenotype and function4. Given that it is widely accepted that any human conventional CD4+ T cell can upregulate FoxP3 upon activation in the presence of IL-2 without suppressive capacities5-9, inventors have demonstrated that not all FoxP3 expressing CD4+ T cells in PBMCs have regulatory function. Indeed, FoxP3+CD4+ T cells can be divided in (1) naïve/resting Treg cells with a CD127lowCD25++CD45RA+FoxP3low phenotype (nTreg) and (2) effector/activated Treg with CD127lowCD25+++CD45RA-FoxP3high phenotype (eTreg), both of which being highly suppressive in vitro, and (3) CD4+ T cells that are not suppressive with a CD127lowCD25++CD45RA-FoxP3low phenotype. Inventors could also show that naïve Treg cells bearing thymic emigrant markers were precursors of effector Treg cells10.
The relevance of this functional delineation of FoxP3 expressing CD4+ T cells could be verified in immune mediated diseases systemic lupus erythematosus (SLE) and sarcoidosis as each subset were abnormal in PBMCs as eTreg cells were markedly increased in sarcoidosis while non Treg FoxP3low cells were highly increased in active SLE10.
Because the aforementioned classification was made on the analysis of intracellular FoxP3 expression, inventors sought to determine specific surface markers for FoxP3 expressing cells subsets. While nTreg cells can be easily defined by the CD127lowCD25++CD45RA+FoxP3low phenotype11-13, it is still unknown how to differentiate FoxP3low non Treg cells from FoxP3high Treg cells based on the use of surface markers.
Other groups have shown that human Treg cells could be subdivided based on the expression of ICOS14, HLA-DR15 or intracellular expression of Helios16, the latter being reported as specific for natural Treg cells.
However, there remains an unmet need in the art for specific surface markers for the effector/activated Treg.
The inventors therefore sought to correlate the expression of the latter surrogate differentiating markers with the expression level of FoxP3 and other surface markers.